Answer 1

The words says it all !
Cancate means to connect two Literal Strings in one it uses plus(+) operator as a connections in middle of two strings .
Example Below:
\\asuming we are in the main method in java
String s1 = "Hello";
String s2 = "World";
System.out.println(s1.concate(s2));
and this gonna print in console like this: HelloWorld
method concate is part of java api and you can find many string methods in java api:https://docs.oracle.com/javase/7/docs/api/java/lang/String.html

\\We can concate two literal string as below:

System.out.println("Hello"+"World");
\\and the line below gonna print the same as the method used below